There is known a seat frame including: a seat cushion frame for supporting a seat cushion of a seat of a vehicle; and a seat back frame to which a retractor (seat belt retaining member) is coupled, the seat back frame being coupled to the seat cushion frame, and supporting a seat back of the seat. Patent Literature 1 discloses a seat back frame including: a pipe frame extending along a contour of a seat back; and a tower frame provided so as to extend in an up-and-down direction of a vehicle. To an upper portion of the tower frame of the seat back frame, a belt guide portion is mounted. The belt guide portion guides a shoulder belt for holding a shoulder portion of an occupant. Further, a bracket is fixed to a lower pipe (lower cross member) formed on an inner side of a lower portion of the tower frame, and a retractor (seat belt retaining member) for winding a seat belt is fixed to the bracket.